Today's internal combustion engines must meet ever-stricter emissions and efficiency standards demanded by consumers and government regulatory agencies. Accordingly, automotive manufacturers and suppliers expend great effort and capital in researching and developing technology to improve the operation of the internal combustion engine. Turbochargers are one area of engine development that is of particular interest.
A turbocharger uses exhaust gas energy, which would normally be wasted, to drive a turbine. The turbine is mounted to a shaft that in turn drives a compressor. The turbine converts the heat and kinetic energy of the exhaust into rotational power that drives the compressor. The objective of a turbocharger is to improve the engine's volumetric efficiency by increasing the density of the air entering the engine. The compressor draws in ambient air and compresses it into the intake manifold and ultimately the cylinders. Thus, a greater mass of air enters the cylinders on each intake stroke.
Given that a turbocharger must handle exhaust straight from the engine, it can be appreciated that the components of a turbocharger are subjected to extreme temperatures. Many turbocharger components have been designed to handle extreme heat, particularly on the turbine side of the turbocharger. However, some components are difficult to make temperature resistant while maintaining functionality, such as the moving joints, actuators, and seals associated with variable turbine geometry (VTG) mechanisms and waste gate control mechanisms.
For example, traditional VTG assemblies include an actuator pivot shaft that extends through an actuator flange bushing to connect the actuator to the vane pack and adjustment ring assembly. This traditional design uses piston rings on the pivot shaft as a seal mechanism in order to contain hot, pressurized exhaust gases from leaking to atmosphere. However, the standard piston ring design allows some leakage of exhaust gas to the outside of the turbo assembly. Accordingly, there is a need for a pivot shaft seal that can prevent hot, pressurized exhaust gases from leaking under high heat conditions while still allowing the pivot shaft to rotate.